In order to improve the stability of klystron output characteristics, it is necessary to resist deformations that may affect klystron cavities due to temperature effects.
The background art deals with many constructional implementations of klystron resonant cavities.
Known in the art is a klystron utilizing its cavity assemblies made of oxygen-free copper. Each cavity comprises a body and face walls accommodating drift tubes. In the case of an average-power klystron, heat is applied to the cavities due to the following effects: microwave power loss that occurs in the cavity walls; and partial interception of the electron beam by the drift tubes (cf. U.S. Pat. No. 1,491,421, cl.21g, 13/17, 1963).
Heating the cavities may lead to burning of the ends of the drift tubes, to deformations of the walls, and to a change in the resonant frequencies of the cavities.
To resist the heating, use is made of forced cooling, liquid or air.
There is another kylstron comprising cavities with face walls, which accommodate drift tubes (cf. the USSR Inventor's Certificate No. 266,791, cl. HOlJ 23/20, 1972). In this klystron, higher stability of the output characteristics is attained in the following manner. The portions of the drift tubes in the cavities are provided with an annular slot which is positioned concentrically with the klystron axis, beginning at the end of the drift tube and terminating in the cooled elements of the cavities.
The outer portion of the drift tube is made of a material having a low linear expansion coefficient, for example, molybdenum.
Though the drift tubes are bimetallic, the face walls are yet of considerable thickness. The difference between the linear expansion coefficients of the dissimilar metals causes an extra mechanical stress in the cavity walls. The annular slot causes an increase in the area of the capacitive gap of the cavity, which results in a decrease of its wave resistance, thereby impairing the output characteristics of the klystron. With a klystron having a high power output, there may result a parasitic oscillation since the annular slot approaches a resonance condition in this case.